Apparatus for re-shaping a train of light pulses, and apparatus for recovering a periodic signal synchronized on a train of modulated light pulses

Abstract

Apparatus for reshaping a train of light pulses includes an electro-absorbent modulator to which the train of pulses is applied for the purpose of being resynchronized and reshaped. A periodic signal generator that is adjustable in phase and frequency applies a periodic signal to the modulator to voltage control said modulator. Servo-control means control said generator in phase and in frequency to minimize the mean photocurrent delivered by the modulator while it is both in its absorbent state and receiving a light pulse. The apparatus may also be used to recover a periodic signal that is synchronized on a train of modulated light pulses. The invention is applicable to long distance telecommunications by transmitting soliton pulses along optical fibers.

I claim: 
     
       1. Apparatus for reshaping a train of light pulses, the apparatus comprising: a light modulator to which the train of pulses to be resynchronized and reshaped is applied;   a periodic signal generator that is adjustable in phase and in frequency which applies a periodic signal to the modulator, thereby providing voltage control for said modulator; and   means for synchronizing the generator on the train of modulated light pulses received by the modulator;   wherein the modulator is a modulator of the electro-absorbent type generating a photocurrent while it is in an absorbent state and is receiving a light pulse; and   wherein the means for synchronizing the generator include servo-control means for controlling the phase and frequency of said generator, for minimizing the mean photocurrent as generated by the modulator while it is in its absorbent state and receiving a light pulse, thereby reshaping and resynchronizing the train of pulses.   
     
     
       2. Apparatus according to claim 1, wherein an amplifier is disposed at the output from the modulator. 
     
     
       3. Apparatus according to claim 1, wherein an optical bandpass filter is disposed at the output from the modulator. 
     
     
       4. A long distance optical fiber telecommunications system comprising: generator means for generating trains of modulated light pulses;   detector and decoder means for detecting and decoding said pulses;   an optical fiber circuit for propagating pulses from the generator means to the detector and decoder means; and   at least one repeater apparatus according to claim 1 for in-line reshaping of the trains of light pulses.   
     
     
       5. A telecommunications system according to claim 4, for transmitting data by means of soliton pulses, wherein the periodic signal generator of the repeater apparatus delivers periodic signals shaped for reshaping the light pulses into soliton pulses. 
     
     
       6. Apparatus for recovering a periodic signal synchronized on a train of modulated light pulses, the apparatus comprising: a periodic signal generator that is adjustable in phase and in frequency;   electro-optical means that receive the light pulses and that emit a corresponding electrical signal; and   means for servo-controlling the phase and the frequency of the generator as a function of said electrical signal so as to cause the generator to deliver the synchronized signal;   wherein the electro-optical means include an electro-absorbent modulator which is voltage controlled by the synchronized periodic signal delivered by the generator; and   wherein the servo-control means control the generator in such a manner that the mean photocurrent delivered by the modulator while in its absorbent state and receiving a light pulse is minimized.